What pitch chain?

[HoosierDeereMan]

My 340/S has the stock gearing with a 17 upper and 39 lower sprocket and 74 pitch chain. My top speed is about 65 MPH. With my present set up I can spin the track out from under it on low end. I would like to try a 21 tooth upper sprocket as that is what the 340 Dator, Cyclone, and Liquifire used to increase my top end speed. My question is how do I determine what pitch chain I need? If I increase my top gear by 4 teeth do I need a chain that is 4 pins longer? Would a 78 pitch chain work? Confused and at a loss!

Troy

[lwb140]

so mathematically if rpm remains the same the 19/35 should be about 79 mph , about what rpm will your sled max out at ? at 65 mph ? wade

[HoosierDeereMan]

8100 to 8200 RPM.

Troy

[JDGuy]

Troy: I do not recall where I found this years ago. I used it on some gearing changes on a '87 Cat tiger 6 back in the day and the formula worked correctly for me. Suggest you confirm it by running it for your current setup.

Guy

For linkbelt type chain:
(CD X 2)/0.375 + (TS + BS)/2 = Pitch
CD= Center distance
TS= Top sprocket no. of teeth
BS= Bottom sprocket no. of teeth
Round off formula result to next highest even pitch no.

For example, if formula calculates 68.67, use 70 pitch chain.
if formula caluates 68.0, use 70 pitch chain, ie. there is no chain slack in formula.

[lwb140]

the cd on a 340/s is 8 1/2 inches , so does the .375 represent the distance between chain pins ? wade

[JDGuy]

Wade: That was my guess also (0.375 = distance between chain pins, center to center), there was no additional info with the formula than what I posted above. Still cannot remember where I originally found it, may have been a mid-80's Cat performance manual ???

Guy

[HoosierDeereMan]

Guy,

Sorry for not getting back to this thread before now. Been busy with getting ready and riding on the UP trip. Thanks for all the chain info. It's a huge help!

Troy